1. Field of the Invention
This invention generally relates to measuring process variables in a processing system. More specifically, the present invention relates to a sensor system for measuring process variables in the machine direction, with cross direction averaging, in a continuous flat sheet process such as a paper making process.
2. Background Art
In many continuous flat sheet formation processes such as paper making, properties of the sheet material can be tracked in two perpendicular directions: the machine direction (MD), which is the direction of movement of the sheet material during production; and cross machine direction (CD), which is perpendicular to the MD or across the sheet during production.
In these continuous flat sheet processes, it would be desirable to track the change of certain process variables along the machine direction to produce gradients that can be used for monitoring, control, and optimization. Measurements of the process can be made by fixing a series of sensors, typically designed for scanning systems, on fixed brackets in corresponding cross direction locations along the machine length. Due to their scanner based heritage, the measurement windows (sampling apertures) are very small in comparison to the width of the process, however the true machine direction measurement is really a process average of the entire cross direction width. Sampling a very small percentage of the sheet leads to a technical problem where cross direction variations would significantly influence the results of machine direction gradients due to sensor alignment, sheet wander, local streak generation, etc.